1. Field of the Invention
This invention relates to nonwoven webs of thermoplastic fibers and their manufacture. More particularly, the invention relates to lightweight nonwoven webs having attributes of softness, strength and appearance especially suitable for applications such as disposable diaper liners, wrappers for sanitary napkins, and the like. Such webs may be formed by melting a thermoplastic material and spinning it to form filaments or fibers which are collected and interbonded at desired basis weights. To be useful for the identified applications as well as others, the web is desirably sufficiently porous to allow waste material deposited on the product, for example, a disposable diaper to pass through and yet strong enough to prevent disintegration of the web. In addition, the web should be attractive in appearance and sufficiently opaque to cover discoloration and the like. Finally, for comfort the web should be soft and flexible as well as nonirritating.
2. Description of the Prior Art
Nonwoven materials of the type generally described have been available for years and have been the subject of intensive investigation, particularly since the development and widespread use of disposable diapers. It is known, and conventional, for example, to utilize spunbonded polymeric filament webs in the basis weight of about 1 oz/yd.sup.2 or less as a liner for disposable diapers. Further, other materials such as bonded carded webs, fibrillated films, and scrimlike materials of low basis weight have been so used. It is also known that some appearance and functional aspects of nonwoven diaper liners can be improved by embossing the web to produce more or less permanent deformation.
Examples of such disclosures include U.S. Pat. No. 4,041,951 to Sanford, U.S. Pat. No. 3,616,157 to Smith, Canadian Pat. No. 820,104 to Paulig and Taylor, U.S. Pat. No. 3,814,101 to Kozak, and U.S. Pat. No. 4,050,462 to Woon and Endres.
In general, however, selection of a nonwoven facing material has involved a compromise between desirable physical and functional attributes and comfort and appearance factors. Furthermore, cost considerations have fostered a tendency to seek lighter basis weight materials. Consequently a need has been demonstrated for a light basis weight nonwoven facing material having adequate strength and having softness and bulk without deterioration of desirable physical properties.